Albion were undone by a 90th-minute equaliser as Barnsley secured a 1-1 draw and a share of the spoils in their Boxing Day clash.
Aapo Halme converted from close range late on to cruelly deny the Baggies although Albion extended their unbeaten run to 14 matches - the club's longest sequence since 1957.
Albion had looked on course for their first victory at Oakwell since 1947, a run stretching back 18 meetings, courtesy of Filip Krovinović's fifth-minute strike.
The Croatian capitalised on a mis-hit clearance by Tykes goalkeeper Sami Radlinger to convert from long range and register his first goal of the season - becoming Albion's 15th different scorer of the campaign so far.
Yet Albion were also indebted to a superb display from Sam Johnstone as he pulled off a string of fine saves while Tykes defender Mads Andersen headed against the crossbar during the first period.
The draw extends Albion's impressive away record, with the top-of-the-table Baggies, who were backed by 3,579 travelling supporters for the festive encounter in South Yorkshire, now unbeaten in seven on the road.
Slaven Bilić made four changes from the 1-1 draw against Brentford, Krovinović coming in alongside fit-again Kieran Gibbs, Ahmed Hegazi and Charlie Austin.
And it took the midfielder just a matter of minutes to make an impact, capitalising on Radlinger's scuffed clearance to convert high beyond the Tykes goalkeeper as he rushed back into an empty net.
Johnstone was first called upon to make two superb saves midway through the opening period, spreading himself to deny Cauley Woodrow before tipping over from Jacob Brown minutes later.
Andersen headed against the crossbar just before the half-hour mark as the hosts pushed for a leveller.
Baggies skipper Jake Livermore sent a long-range strike narrowly off target at the other end before Austin was denied by Radlinger as he latched on to a loose defensive header back to the keeper.
Yet there was still time for Johnstone to come to Albion's rescue again on the stroke of half-time, saving well at his near post from Conor Chaplin to preserve the visitors' advantage heading into half-time.
The Baggies No.1 was at it yet again in the 57th minute, diving to his right to push away Luke Thomas' strike from distance.
Bilić introduced Kenneth Zohore and Gareth Barry as the second half wore on, unfortunately losing Kieran Gibbs to injury late on.
And there was worse to come just moments later as Halme converted from close range for the Tykes to ensure it finished all square, with Albion now looking to get back to winning ways at home to Middlesbrough on Sunday.
Albion: Johnstone, Furlong, Ajayi, Hegazi, Gibbs (Townsend 89), Sawyers, Livermore, Krovinović (Barry 77), Pereira, Robson-Kanu, Austin (Zohore 62).
Subs: Bond, O'Shea, Edwards, Phillips.